Airline safety is of great concern to public. Tragically, there have been a number of incidents where an otherwise survivable accident has had fatal results due to ignition of the interior of the aircraft caused by burning jet fuel external to the aircraft. While airports in particular are well staffed and equipped to fight fires, there is often a brief time delay before fire terminating measures can be put in place, simply because the equipment is not at the location of the fire. In such a circumstance, the difference of a few short minutes in prevention of burnthough of the fuselage of an aircraft can save lives and property in a postcrash fire accident in which the fuselage remains intact. See, e.g. the report to the FAA (Federal Aviation Administration) entitled “Full-Scale Test Evaluation of Aircraft Fuel Fire Burnthrough Resistance Improvements” by Timothy R. Marker. DOT/FAA/AR-98/52 January 1999, Final Report. Additionally, the FAA is adopting upgraded flammability standards for thermal and acoustic insulation material used in transport category airplanes. The federal regulation FAR 25.856(b) applies to insulation materials installed in the lower half of the fuselage because that area is most susceptible to burnthrough from an external fuel fire, and applies to aircraft having a passenger capacity of 20 or greater. Similarly, there have been a number of fire accidents on ships and on offshore drilling platforms in which prevention of burnthough of structures can save lives and property.
Blankets have previously been suggested for use in providing thermal and/or acoustic insulation in aircraft and other vehicles to shield passengers from noise and temperature extremes. See U.S. Pat. No. 5,759,659, which describes an insulation blanket that includes fibrous insulation, foam insulation, or a combination thereof encased within a heat-sealable polymer comprising a rubber-toughened thermoplastic polyolefin. The thermoplastic polyolefin is described as preferably being flame retardant as well. See column 4, lines 14-26, which notes that flame retardancy may be achieved by blending the thermoplastic polyolefin with one or more flame retardant agents including intumescent materials, e.g., “expanding graphite.” The blanket additionally comprises a high temperature resistant layer 16 as part of the construction, such as ceramic paper, woven ceramic fibers, woven fiberglass fibers, ceramic non-woven scrims, and fiberglass non-woven scrims. See column 5, lines 52-65. Similar burn through resistant nonwoven mats are described in U.S. Pat. No. 6,551,951. The mat is made up of non-respirable and/or biosoluble base fibers that are stated to be capable of retaining their integrity and dimensional stability during 4 minutes of exposure to a fluctuating high pressure flame front at a temperature of 1100° C. Examples given of non-respirable base fibers which make up the nonwoven mat are quartz fibers; aluminosilicate, aluminoborosilicate or alumina ceramic oxide fibers; partially oxidized pitch based fibers; and partially oxidized polyacrylonitrile fibers having mean diameters greater than 6 microns. See the Abstract.
Laminate sheet materials for fire barrier applications are described in U.S. Pat. No. 6,670,291. The laminate comprises a first layer comprised of polymeric material and a second layer comprised of non-metallic fibers. See the Abstract. The second layer may be, for example, a laminate may comprise vermiculite coated paper having metal oxide coated regions thereon, available from the 3M Company under the trade designation “NEXTEL Flame Stopping Dot Paper.” See column 17, lines 50-55.
Flexible graphite is a well-known material used in a variety of industrial, commercial and domestic applications because of its chemical inertness and unique electrical and thermal conduction properties. It is of particular use as a gasketing or sealing material in automobile engines, piping flanges and vessel joints and as a fire proof covering for walls or floors. See U.S. Pat. No. 6,245,400.
A method for making expandable graphite particles is described in U.S. Pat. No. 3,404,061, wherein graphite flakes are intercalated by dispersing the flakes in a solution containing an oxidizing agent e.g., a mixture of nitric and sulfuric acid. Upon exposure to high temperature, the particles of intercalated graphite expand in dimension as much as 80 to 1000 or more times its original volume in an accordion-like fashion in the c-direction, i.e. in the direction perpendicular to the crystalline planes of the constituent graphite particles. The exfoliated graphite particles are vermiform in appearance, and are therefore commonly referred to as worms. The worms, i.e. expanded graphite, may be compressed together into flexible sheets which, unlike the original graphite flakes, can be formed and cut into various shapes for gasket and sealing purposes.
An alternative embodiment of a flexible graphite sheet is made in U.S. Pat. No. 6,143,218 by compressing a mixture of fine particles of intercalated, exfoliated, expanded natural graphite with fine particles of intercalated, unexpanded, expandable particles of natural graphite, the unexpanded particles being more finely sized than the expanded particles. The resulting sheet of flexible graphite is stated to exhibit improved fire retardant and sealability properties.
Filmy graphite materials are described in US Patent Application No. 2007/0032589 (the “'589 application”). In the background section of this application, it is pointed out that a process has been developed in which a special polymer film is graphitized by direct heat treatment (hereinafter, referred to as a “polymer graphitization process”). Examples of the polymer film used for this purpose include films containing polyoxadiazole, polyimide, polyphenylenevinylene, polybenzimidazole, polybenzoxazole, polythiazole, or polyamide. The '589 application goes on to describe a method for providing a thick filmy graphite having excellent physical properties using a short-time heat treatment at relatively low temperatures. In this application, it was noted that by controlling the molecular structure and molecular orientation of the polyimide (particularly the birefringence or coefficient of linear expansion), transformation into a quality graphite is enabled.